English

Classifying invariant $\sigma$-ideals with analytic base on good Cantor measure spaces

General Topology 2016-02-19 v1 Dynamical Systems Logic

Abstract

Let XX be a zero-dimensional compact metrizable space endowed with a strictly positive continuous Borel σ\sigma-additive measure μ\mu which is good in the sense that for any clopen subsets U,VXU,V\subset X with μ(U)<μ(V)\mu(U)<\mu(V) there is a clopen set WVW\subset V with μ(W)=μ(U)\mu(W)=\mu(U). We study σ\sigma-ideals with Borel base on XX which are invariant under the action of the group Hμ(X)H_\mu(X) of measure-preserving homeomorphisms of (X,μ)(X,\mu), and show that any such σ\sigma-ideal I\mathcal I is equal to one of seven σ\sigma-ideals: {}\{\emptyset\}, [X]ω[X]^{\le\omega}, E\mathcal E, MN\mathcal M\cap\mathcal N, M\mathcal M, N\mathcal N, or [X]c[X]^{\le \mathfrak c}. Here [X]κ[X]^{\le\kappa} is the ideal consisting of subsets of cardiality κ\le\kappa in XX, M\mathcal M is the ideal of meager subsets of XX, N={AX:μ(A)=0}\mathcal N=\{A\subset X:\mu(A)=0\} is the ideal of null subsets of (X,μ)(X,\mu), and E\mathcal E is the σ\sigma-ideal generated by closed null subsets of (X,μ)(X,\mu).

Keywords

Cite

@article{arxiv.1409.3922,
  title  = {Classifying invariant $\sigma$-ideals with analytic base on good Cantor measure spaces},
  author = {Taras Banakh and Robert Ralowski and Szymon Zeberski},
  journal= {arXiv preprint arXiv:1409.3922},
  year   = {2016}
}

Comments

10 pages

R2 v1 2026-06-22T05:55:52.361Z